Alkyl aromatic compounds form important chemicals which may be utilized as intermediates in many industrial applications as, for example, polymeric material, plasticizers, detergents, etc. Heretofore, the production of alkyl aromatic compounds has been effected by alkylating an aromatic compound with an alkylating agent in the presence of acidic catalysts. These acidic catalysts include sulfuric acid and hydrofluoric acid due to the relatively good activity for the purpose intended. However, the use of these liquid acids such as sulfuric acid or hydrofluoric acid has inherently some drawbacks or shortcomings. The acids hereinbefore named are extremely corrosive in nature, thus requiring special handling and equipment due to the dangerous nature thereof. In addition, the use of these acids might also involve some environmentally hazardous problems which are attendant thereto. Therefore, it would be preferable to utilize a safer and more simple catalyst, preferentially in solid state, in a fixed bed reactor to produce the desired compounds. The use of a simpler process would result in less capital investment and therefore enable the producer to provide a less expensive product.
In view of this we have now discovered that a solid alkylation catalyst may be employed to effect the desired alkylation to obtain a production which is equal in quality to those products obtained when utilizing liquid acidic catalyst while also improving the activity of the catalyst as well as the selectivity of the product.
Prior patents have described the use of solid catalysts comprising clays which contain a metallic component. For example, U.S. Pat. No. 4,499,319 discloses a cation-exchanged layered clay in which a layered clay having a lamellar structure is ion-exchanged with a metallic cation. The catalyst is then activated by heating in air at a temperature in the range of from about 80.degree. to 200.degree. C. The catalyst may be used to alkylate aromatic compounds with an alkylating agent containing less than about 6 carbon atoms. U.S. Pat. No. 4,749,808 also uses a metal cation-exchanged clay to produce an ester by reacting an olefin or an olefin oxide with a carboxylic acid. U.S. Pat. Nos. 3,849,507 and 4,605,806 both utilize hydrogen ion-exchanged layered clays as catalysts for producing esters in a manner similar to that set forth in the above-enumerated patents.
U.S. Pat. No. 3,962,361 utilizes an ion-exchanged synthetic saponite clay for acid catalyzed reactions in which the clay is ion-exchanged with a metal cation and activated by heating to a temperature less than 200.degree. C. Likewise, U.S. Pat. No. 3,965,043 similar discloses an ion-exchanged natural clay for use in alkylating aromatic hydrocarbons similar to the prior named patent. Other U.S. patents which disclose alkylating catalysts which are solid in nature include U.S. Pat. Nos. 3,979,331, 4,046,826 and 4,075,126. These patents disclose alkylation of aromatic compounds with a synthetic clay which has been cation-exchanged and activated.
It is to be noted that many of the prior patents which have been discussed employ clays which have been subjected to a process whereby a metal cation is exchanged for the hydrogen ions normally present in the clay. The catalyst of the present invention which we have discovered comprises a clay in which a metal cation is impregnated throughout the clay rather than having the ion exchanged thereon. This catalyst will possess excellent characteristics with regard to the activity of the catalyst as well as to the selectivity of the product which is obtained by the reaction.